From looking at the instructions to remove the upper part of the case, I would say that the chances of a Silver MacNTouch fitting is pretty good. The builtin keyboard looks like it would be removed in a similar manner as in the Oct2005 PowerBook (http://www.ifixit.com/Guide/64.4.0.html).

Good... LORD! I knew I was spoiled with my TiBook, but I didn't know keyboard removal was THAT bad for the new machines!

But now I've got a MacBook, with exactly zero chance of replacing the keyboard, even if I came into posession of a MacNTouch. :-/ Maybe somebody will come up with a hack to get better gesture recognition out of the trackpad...

You should get some useful error message from the following procedure:
(As I am with Windows, I can't be sure about details but I know you can do that with Java.)

Create a shell script in the folder where your FW utility has been installed. (You should see there a file named lax.jar.)
Copy&Paste this launch code into a shell script named something like mu.sh and make it executable (i.e. chmod a+x mu.sh)

Exception in thread "main" java.lang.UnsatisfiedLinkError: no jusbMacOSX in java.library.path
at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1682)
at java.lang.Runtime.loadLibrary0(Runtime.java:822)
at java.lang.System.loadLibrary(System.java:992)
at usb.macosx.MacOSX.getHost(MacOSX.java:86)
at usb.macosx.MacOSX.createHost(MacOSX.java:59)
at usb.core.HostFactory.maybeGetHost(HostFactory.java:141)
at usb.core.HostFactory.getHost(HostFactory.java:124)
at fingerworks.firmup.k.<init>(Unknown Source)
at fingerworks.firmup.UtilityLauncher.<init>(Unknown Source)
at fingerworks.firmup.UtilityLauncher.main(Unknown Source)

Minox wrote:Exception in thread "main" java.lang.UnsatisfiedLinkError: no jusbMacOSXin java.library.path at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1682)(...)Now the app launches but doesn't see the macntouch

Java and you said exactly the same thing, each with his own words!

* USBJava Native Interface library is missing

That means that we have to find a jusbMacOSX.so library file (the Unix flavor of Dynamically Linked Library)...

The catch is that USB handling may have changed for the version of Java currently installed with Mac OS.
This means that we have to find someone who can dig one step further on this platform...